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Mateusz Pusz
efbc844199
* Fix #580: use fixed-point arithmetic for integer unit conversions Introduce a fixed-point implementation for unit conversions involving integer representations, avoiding loss of significant digits that previously occurred when the conversion factor was not a whole number. New files: - src/core/include/mp-units/bits/fixed_point.h: double_width_int<T> and fixed_point<T,n> types for exact rational scaling of integer values. Uses __int128 when available (__SIZEOF_INT128__) for 64-bit integers. - src/core/include/mp-units/framework/scaling.h: public scaling_traits<> customization point and scale<To>(M, value) free function. Provides built-in specializations for floating-point and integer-like types. - test/static/fixed_point_test.cpp: static assertions for the new types. - test/runtime/fixed_point_test.cpp: runtime arithmetic edge-case tests. Modified: - sudo_cast.h: replace hand-rolled conversion_value_traits / sudo_cast_value machinery with a single scale<To::rep>(c_mag, ...) call. - representation_concepts.h: add MagnitudeScalable concept; replace ComplexScalar with HasComplexOperations (which is its definition). - customization_points.h: add unspecified_rep tag and declare the primary scaling_traits<> template. - framework.h / CMakeLists.txt: wire in the new headers. - hacks.h: add MP_UNITS_DIAGNOSTIC_IGNORE_PEDANTIC and MP_UNITS_DIAGNOSTIC_IGNORE_SIGN_CONVERSION macros. - example/measurement.cpp: add scaling_traits specializations for measurement<T> to demonstrate the customization point. - test/static/{international,usc}_test.cpp: disable two tests that are blocked on issue #614. Co-authored-by: Tobias Hanhart <burnpanck@users.noreply.github.com> * Fix value_Type typo in floating_point_scaling_factor_type specialization The partial specialization for types with a nested value_type used 'value_Type' (capital T) instead of 'value_type', making the entire specialization dead code as the requires-clause could never be satisfied. Also fix 'mantiassa' -> 'mantissa' in the adjacent comment. * Fix docstring typos in scaling_traits documentation - 'quantitiy' -> 'quantity' - 'dictatet' -> 'dictated' - 'convetrible' -> 'convertible' - 'implemenation' -> 'implementation' - 'availabe' -> 'available' * Fix conflict resolution error: keep ComplexScalar name from master When resolving the merge conflict in representation_concepts.h, the PR's renamed version of the concept ('HasComplexOperations') was used instead of master's established name ('ComplexScalar'). The two concepts are semantically equivalent — burnpanck simply renamed it in his branch. Revert to the canonical 'ComplexScalar' name while retaining the new 'MagnitudeScalable' concept which was the actual addition from the PR. * Fix measurement.cpp: remove duplicate class definition from merge The PR branched from a version where measurement<T> was defined inline in measurement.cpp. Master later moved the class to example/include/ measurement.h and changed measurement.cpp to #include that header. The squash merge therefore introduced a duplicate definition: the class from the header and the PR's inline class were both visible, causing an 'ambiguous reference' error. Remove the now-redundant inline class; the scaling_traits specializations added by the PR work correctly with the class from measurement.h. * style: pre-commit * docs: chapters anchors improved in the "custom representation" chapter * docs: value conversions chapter improved * refactor: scaling support refactored * fix: clang-16 crash fixed * docs: `measurement` example documentation updated to match changes * fix: use exact wide-integer arithmetic for rational unit conversions on all platforms On ARM / Apple Silicon, long double == double (64-bit mantissa). The old fixed_point<T>(long double) initialiser lost ~12 bits of precision for 64-bit integer types when representing the scaling ratio, producing an error of ~49 units for the 10/9 (degree → gradian) conversion with a 10^18 input value. Fix by splitting the integer-path else-branch into two cases: • Pure rational M (is_integral(M * (denominator(M) / numerator(M))) == true): use (value * numerator) / denominator via double_width_int_for_t<> arithmetic. This is exact on every platform regardless of long double width. • Irrational M (involves π etc.): keep the long double fixed_point approximation. These conversions are inherently approximate; small values still produce correct truncated results on all platforms. Update the test comment to reflect the new exact-arithmetic path. Fixes CI failures on clang-18/ARM and apple-clang-16. * fix: replace floating-point TeX-point test with exact integer equivalent 72.27 is not exactly representable as double (it rounds to 72.2699...96). Multiplying by the conversion factor 100/7227 via long double gives a result ≥ 1.0 on x86 (80-bit long double, 64-bit mantissa) only by chance, but 0.99999...978 on ARM / Apple Silicon where long double == double (52-bit). The correct mathematical statement is: 7227 tex_point = 100 inch (exact rational relationship). Use that integer form instead of the inexact 72.27 double literal so the test is correct and platform-independent. --------- Co-authored-by: Tobias Hanhart <burnpanck@users.noreply.github.com>
98 lines
4.1 KiB
C++
98 lines
4.1 KiB
C++
// The MIT License (MIT)
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//
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// Copyright (c) 2018 Mateusz Pusz
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//
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// Permission is hereby granted, free of charge, to any person obtaining a copy
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// of this software and associated documentation files (the "Software"), to deal
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// in the Software without restriction, including without limitation the rights
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// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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// copies of the Software, and to permit persons to whom the Software is
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// furnished to do so, subject to the following conditions:
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//
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// The above copyright notice and this permission notice shall be included in all
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// copies or substantial portions of the Software.
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//
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// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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// SOFTWARE.
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// !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
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// !!! Before you commit any changes to this file please make sure to check if it !!!
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// !!! renders correctly in the documentation "Examples" section. !!!
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// !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
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#include "measurement.h"
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#include <mp-units/bits/hacks.h>
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#include <mp-units/compat_macros.h>
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#ifdef MP_UNITS_IMPORT_STD
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import std;
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#else
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#include <iostream>
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#endif
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#ifdef MP_UNITS_MODULES
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import mp_units;
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#else
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#include <mp-units/framework.h>
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#include <mp-units/math.h>
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#include <mp-units/systems/isq/space_and_time.h>
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#include <mp-units/systems/si.h>
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#endif
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template<typename T, typename U>
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struct mp_units::scaling_traits<measurement<T>, measurement<U>> {
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template<auto M>
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[[nodiscard]] static constexpr measurement<U> scale(const measurement<T>& value)
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{
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return measurement<U>(mp_units::scale<U>(M, value.value()), mp_units::scale<U>(M, value.uncertainty()));
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}
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};
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static_assert(mp_units::RepresentationOf<measurement<int>, mp_units::quantity_character::real_scalar>);
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static_assert(mp_units::RepresentationOf<measurement<int>, mp_units::quantity_character::vector>);
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static_assert(mp_units::RepresentationOf<measurement<double>, mp_units::quantity_character::real_scalar>);
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static_assert(mp_units::RepresentationOf<measurement<double>, mp_units::quantity_character::vector>);
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void example()
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{
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using namespace mp_units;
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using namespace mp_units::si::unit_symbols;
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std::cout << "Mass of the Sun: M_sun = " << measurement{19884, 2} * (mag_power<10, 26> * kg) << '\n';
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const auto acceleration = isq::acceleration(measurement{9.8, 0.1} * m / s2);
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const auto time = measurement{1.2, 0.1} * s;
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const QuantityOf<isq::velocity> auto velocity = acceleration * time;
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std::cout << "Velocity calculation: V = " << acceleration << " * " << time << " = " << velocity << " = "
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<< velocity.in(km / h) << '\n';
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const auto length = measurement{123., 1.} * m;
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std::cout << "Scalar multiplication: d = 10 * " << length << " = " << 10 * length << '\n';
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const auto radius = measurement{5.0, 0.1} * m;
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const auto circumference = radius * (mag<2> * π);
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const auto area = pow<2>(radius) * π;
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std::cout << "Radius: r = " << radius << '\n';
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std::cout << "Circular circumference: 2πr = " << circumference << " = " << circumference.in(m) << '\n';
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std::cout << "Circular area: πr² = " << area << " = " << area.in(m2) << '\n';
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const auto area_measured = measurement{25.0, 1.0} * π * m2;
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const auto radius_from_area = sqrt(area_measured / π);
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std::cout << "Radius from area: A = " << area_measured << " -> r = √(A/π) = " << radius_from_area << '\n';
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}
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int main()
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{
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try {
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example();
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} catch (const std::exception& ex) {
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std::cerr << "Unhandled std exception caught: " << ex.what() << '\n';
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} catch (...) {
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std::cerr << "Unhandled unknown exception caught\n";
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}
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}
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